swift234

Remove a circular dependency AST<->Sema caused by type printing

AST used to depend on Sema in type printing.  Specifically,
TypeVariableType::printImpl() is inside Sema.

This change moves the type variable identifier from
TypeVariableType::Implementation to TypeVariableType. This enables us to print
type variables in AST library.

Because type variable type is a temporary type for use inside type checker
only, I don't expect that we will modify it to be more verbose to enhance
diagnostics.  This is a job for locator printing.


Swift SVN r8559